Exploring the Thalamus and Its Role in Cortical Function

Abstract

Examines the two-way relationships between the thalamus and the cerebral cortex; with updated material and a new chapter on the link between perception and action. The thalamus plays a critical role in perceptual processing, but many questions remain about what thalamic activities contribute to sensory and motor functions. In this book, two pioneers in research on the thalamus examine the close two-way relationships between thalamus and cerebral cortex and look at the distinctive functions of the links between the thalamus and the rest of the brain. Countering the dominant "corticocentric" approach to understanding the cerebral cortex—which does not recognize that all neocortical areas receive important inputs from the thalamus and send outputs to lower motor centers—S. Murray Sherman and R.W. Guillery argue for a reappraisal of the way we think about the cortex and its interactions with the rest of the brain. The book defines some of the functional categories critical to understanding thalamic functions, including the distinctions between drivers (pathways that carry messages to the cortex) and modulators (which can change the pattern of transmission) and between first-order and higher-order thalamic relays—the former receiving ascending drivers and the latter receiving cortical drivers. This second edition further develops these distinctions with expanded emphasis throughout the book on the role of the thalamus in cortical function. An important new chapter suggests a structural basis for linking perception and action, supplying supporting evidence for a link often overlooked in current views of perceptual processing.

Thalamocortical Relations

“…One that is especially important to thalamic relay cells involves T -type Ca 2ϩ channels. (For details of T channel properties, see Huguenard & McCormick, 1994 ;Jahnsen & Llin á s, 1984a, 1984b ; and for other voltage gated channels in thalamic neurons, see Huguenard & McCormick, 1994 ;Sherman & Guillery, 2006 .) The properties of these T channels are qualitatively the same as those of Na ϩ channels involved with the action potential.…”

“…This plus the opening of various slower K ϩ channels (channels that do not inactivate because they have only an activation gate), which produces a hyperpolarizing outward flow of K ϩ , repolarizes the membrane to near its starting position (Figure 10.1D ). However, despite being repolarized, I Na (Sherman and Guillery, 2006) from data supplied by P Smith, K Manning and D Uhlrich. Abbreviations: As in Figure 10.1, plus IC, internal capsule.…”

“…D: Even though the initial resting potential is reached, the Na + channel remains inactivated, because it takes roughly 1 msec ("roughly" having the same meaning as above) of hyperpolarization for de-inactivation. E: Membrane voltage changes showing action potential corresponding to the events in A to D. Redrawn from Figure IV-4 of (Sherman and Guillery, 2006). remains inactivated because it takes roughly 1 msec of this hyperpolarization to open the inactivation gate, restoring the initial conditions of Figure 10.1A .…”

“…Thus, this property of all -or -none Ca 2ϩ spiking based on T channels is fairly unique to the thalamus. Every relay cell of every nucleus in every mammalian species so far tested shows this property (Sherman & Guillery, 2006 ).…”

“…For details of the thalamus beyond the scope of this chapter, see recent books on this topic by Jones ( 2007 ) and Sherman and Guillery ( 2006 ).…”